1. Field of the Invention
The present invention relates to a waterfastness-imparting agent comprising a cationic water-soluble resin having a specific structure, an ink composition containing the waterfastness-imparting agent, a reaction solution containing the waterfastness-imparting agent, and ink jet recording methods using the same.
2. Background Art
Realization of images having good waterfastness and lightfastness and, at the same time, having no significant feathering or bleeding is important for printing of images using ink compositions.
In order to realize good waterfastness, as exemplified below, a combination of a cationic resin with an anionic dye has hitherto been used.
For example, Japanese Patent Laid-Open No. 119280/1987 discloses an ink comprising a hydroxyethylated polyethyleneimine polymer and a dye component. This publication describes that the combination of the hydroxyethylated polyethyleneimine polymer with the dye component can develop waterfastness. Japanese Patent Publication No. 91494/1995 discloses an ink comprising a hydroxyalkylated polyallylamine polymer and a dye. This publication describes that the combination of the hydroxyalkylated polyallylamine polymer and the dye can develop waterfastness. In these two inks, however, a further improvement is required to ensure satisfactory waterfastness of printed images because hydroxyalkyl groups having high hydrophilicity are contained in the polymer.
Japanese Patent Laid-Open Nos. 255876/1990, 296878/1990, and 188174/1991 disclose ink compositions comprising a polyamine, with a molecular weight of not less than 300, having primary amino groups, an anionic dye, and a stability-imparting agent. These publications describe that the combination of the primary amino group with the anionic dye can develop waterfastness. Disadvantageously, however, the resins used in these publications strongly attack the dye. Specifically, according to studies conducted by the present inventors, for example, when this ink is allowed to stand at high temperatures, in some cases, the dye is decomposed or otherwise the photodecomposition of the print is accelerated to render the lightfastness lower than that of an ink containing only the dye.
Japanese Patent Laid-Open No. 305011/1995 discloses a water-base ink comprising a basic water-soluble polymer, an anionic dye with the counter ion being a volatile base, and a buffering agent with the counter ion being a volatile base. This publication describes that, in the ink, the volatile base prevents the dissociation of the polymer and, after printing, the volatile base on paper is evaporated to allow a salt-forming reaction between the polymer and the dye to proceed, thereby developing waterfastness.
Japanese Patent Laid-Open No. 238783/1987 discloses an ink jet recording sheet comprising a homopolymer of an acid salt of diallylamine or an acid salt of monoallylamine or a copolymer of the acid salt of diallylamine with the acid salt of monoallylamine. According to the publication, the advantage of this recording sheet is that the polymer reacts with the dye to become insoluble on the recording medium to develop waterfastness. However, since the ink per se does not have waterfastness, use of a recording medium other than described in the publication cannot develop the waterfastness.
Ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited onto recording media, such as paper, to perform printing. This method has a feature that images having high resolution and high quality can be printed at a high speed by means of relatively inexpensive apparatuses. In general, the ink composition used in the ink jet recording comprises water as a main component and, added thereto, a colorant component and a wetting agent, such as glycerin, for preventing clogging and other purposes.
Furthermore, regarding the ink jet recording method, the application of a polyvalent metal salt solution onto a recording medium followed by the application of an ink composition containing a dye having at least one carboxyl group has been recently proposed (for example, Japanese Patent Laid-Open No. 202328/1993). The advantage of this method is that the polyvalent metal ion combines with the dye to form an insoluble complex, the presence of which can offer an image having waterfastness and high quality free from color bleeding.
Further, the use of a color ink comprising at least a surfactant for imparting a penetrating property or a solvent having a penetrating property and a salt in combination with a black ink capable of being thickened or agglomerated through the action of the salt has been proposed in the art (Japanese Patent Laid-Open No. 106735/1994). The advantage of this method is that high-quality color images having high image density and free from color bleeding can be yielded. Specifically, an ink jet recording method has been proposed wherein two liquids, a liquid containing a salt and an ink composition, are printed to realize good images.
Other ink jet recording methods, wherein two liquids are printed, have also been proposed, for example, in Japanese Patent Laid-Open Nos. 240557/1991 and 240558/1991.
The present inventors have now found that the addition of a cationic water-soluble resin having a specific structure to an ink composition and a reaction solution for use in ink jet recording involving the deposition of two liquids, an ink composition and a reaction solution, onto a recording medium can realize good images, especially images possessing excellent waterfastness and lightfastness, and having no significant feathering or bleeding. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide a waterfastness-imparting agent which can realize an ink composition and a reaction solution for use in ink jet recording method involving the deposition of two liquids, an ink composition and a reaction solution, onto a recording medium, the method being capable of realizing images possessing excellent waterfastness and lightfastness and having no significant feathering or bleeding.
It is another object of the present invention to provide an ink composition which can realize images possessing excellent waterfastness and lightfastness and, at the same time, having no significant feathering or bleeding.
It is a further object of the present invention to provide a reaction solution for use in ink jet recording using two liquids and an ink jet recording method using the same, the method being capable of realizing images possessing excellent waterfastness and lightfastness and having no significant feathering or bleeding, especially having no significant color bleeding.
According to a first aspect of the present invention, there is provided a waterfastness-imparting agent comprising a cationic water-soluble resin, said cationic water-soluble resin comprising a (co)polymer comprising, in formula (I), repeating units (a) represented by formula (a) and repeating units (b) represented by formula (b), the content of the repeating units (a) in the (co)polymer being 100 to 0% by mole, said (co)polymer having in its molecule a carboxyl-containing group as one of the terminal groups and an aromatic ring-containing group as the other terminal group: 
wherein
R1 represents a hydrogen atom or a methyl group;
R2 and R3, which may be the same or different, represent a C1-3 alkyl group;
R4 represents a hydrogen atom or a methyl group;
R5, R6, and R7, which may be the same or different, represent a C1-3 alkyl group;
Zxe2x88x92 represents a counter ion; and
k and l which may be the same or different, are each 1, 2, or 3.
According to a second aspect of the present invention, there is provided an ink composition comprising at least the cationic water-soluble resin as defined above.
According to a third aspect of the present invention, there is provided a reaction solution for use in ink jet recording method involving the deposition of a reaction solution and an ink composition onto a recording medium to perform printing, the reaction solution comprising at least the cationic water-soluble resin as defined above.
According to a fourth aspect of the present invention, there is provided an ink jet recording method comprising the step of depositing an ink composition and a reaction solution onto a recording medium to perform printing, the reaction solution containing a waterfastness-imparting agent which comprises the cationic water-soluble resin having a specific structure as defined above.